The repeatability and reproducibility of the protocol was first examined with a double-blind, randomized protocol in 35 subjects (methodological study group), and after that the administration of research drugs has been open-label. The effects of single doses of two largely endothelium-dependent agents, inhaled salbutamol and intravenous L-arginine, and one endothelium-independent agent, sublingual nitroglycerin, were investigated. However, challenges with the acute dosing of all medical compounds was terminated at the end of December 2016. Thereafter, the measurement protocol has included supine and upright recordings on the tilt-table, followed by supine measurements during paced breathing (15 breaths per minute for 5 minutes, 6 breaths per minute for 5 minutes) that modulate the autonomic nervous tone.